Look at this image, there are normal op-commands I made but the first letter is underlined so I only have to press the key to activate it.

How did I do this? Simple, with the & character before the corresponding letter.
The only side effect is that when you get an input box using %[line] the & character is shown.

This is not exactly new, it's already been in the language files using & but I found that a regular & works just as well, at least for me.
With this you can even rewrite the example.xml with some well placed & and add or move the underlinded anywhere you like for an english dc++.